Method of recording impulses



y 4, 1938. L; T. SACHTLEBEN 2,118,622

METHOD OF RECORDING IMPULSES Filed Jan. 31, 1935 25 Lawrence Sualvfibe 27511 MTm/a/VEM Patented May 24, 1938 UNITED STATES METHOD OF RECORDING IMPULSES Lawrence '1. Sachtleben, Camden, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 31, 1935, Serial No. 4,337

3 Claims.

This invention relates to the art of recording impulses, and more particularly to a method of photographically recording, upon a single-carrier, two or more associated series of sounds which may subsequently be reproduced either separately or together.

Under certain circumstances, it is desirable, and sometimes even necessary,to record two associated series of sounds which may later be reproduced simultaneously to give a combined effeet, or separately. For example, a soloist may wish to have his piano or other accompaniment recorded simultaneously with his own rendition,

but may want the two separable so that each may be individually reproduced for analysis. Similarly, in recording a moving picture scene with explanatory dialogue, it is sometimes desirable to later add a musical background. Many other situations arise in which one desires to record associated audible subject matter, and usually the recordist is limited to a single recording machine and to a single recording medium.

It has already been proposed, in cases of this sort, to run a photographic strip of film through a recorder while exposing it to light fluctuations representative of one set or series of sounds, then to rewind the film and reload it in the recorder, and subsequently again run the film through the recorder while exposing it to light fluctuations representative of another series of sounds somewhat after the manner of so-called double exposure in moving, picture photography. This, however, has met with failure for the reason that the two sets of fluctuations, when recorded along -the same path as heretofore proposed, modify each other and produce results representative of neither one.

The primary object of my invention is to provide a novel method of photographically recording upon a single carrier two or more associated sets of impulses, which method will not be subject to the disadvantage noted heretofore.

More specifically, it is an object of my invention to provide an improved method of photographically recording upon a single carrier and within the space normally allotted for thesound record in accordance with standard practice, as in the case of talking motion picture films, two series of sounds, such as speech and background music, each of which may subsequently be reproduced by itself or in conjunction with the other.

A further object of my invention is to provide a novel method of recording sound as aforesaid in which standard recording practice may be observed with only such slight changes as may be made in any standard photographic recorder.

Another object of my invention is to provide a novel photographic sound record having a plurality of recordings thereon.

In accordance with my invention, which may employ either the so-called variable density method of recording or the variable area method, I record one complete set of sounds on half the Width of the track and record the other complete set of sounds on the second half of the track width. Thus, where the variable area method is employed, for example, the recording beam is first made to vibrate about a mean position midway between one end of recording slit, say the left hand one, and the center thereof to record a right handed sound track, and later (or another recording beam simultaneously) to vibrate about a mean position midway between the right hand end of the slit and the center thereof to record a left-handed sound track. By limiting each track to half the width of the whole track, two separate records are formed each of which can be reproduced alone or together with the other one.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, together with additional objects and advantages thereof will best be understood from the following description thereof, when taken in conjunction with the accompanying drawing in which:

Figure l is a diagrammatic View of a system for forming a sound track in accordance with one form of my invention,

Fig. 2 is a similar view showing how the second sound track is formed, and

Fig. 3 is a fragmentary view of a record resulting from my novel recording method.

Referring more in detail to the drawing, wherein similar reference characters indicate corresponding parts throughout, I have shown, in Figure 1, a variable area recording system comprising a light source I, the filament of which is focused by a condenser 3 at or near a galvanometer mirror 5 adapted to be vibrated in accordance with the sounds or other impulses it is desired to record in a manner well known to those skilled in the art. A light stop I having an aperture 9 therein defined, in part, by the Vertical edges H and i3 is sharpl focused, by means of a lens l5 adjacent the mirror 5, on a second light stop ll. The lens l5 forms an image do of the aperture 9 over the slit 19 in the stop I1, and an objective lens 2| in turn focuses the image So on a strip of film F upon which the record is made as it is fed through the recorder.

The system shown in Figure 2 is, part for part, identical with that shown in Figure l and, in fact, is the same system with a slight change therein. When the system is set up as in Figure 1, the stop I is so disposed that the image I la of the vertical edge ll of the stop 9 will fall substantially midway between the end |9a of the slit l9 and the center thereof to constitute the cutoff edge. Thus, only that portion of the recording beam B which passes between the edges 19a and Ha in a horizontal direction and between the upper and lower edges of the slit [9 in a vertical direction will affect the film F, and, as the film advances and the image edge Ila moves horizontally across the slit IS in response to vibration of the mirror 5, a wavy or variable area record 23 will be formed on the left side of the sound track T, or the space normally allotted to the sound record in talking moving picture film, with the peaks of the waves pointing toward the right side of the track T.

As set up in Figure 2, however, the edge !3 of the aperture 9 is employed as the cut-olf edge and the lens l5 forms an image lilo of the vertical edge 53 midway between the end lb of the slit l9 and the center thereof. In that case, only that portion of the light beam B which passes between the edges l3a and 19b in a horizontal direction and the upper and lower edges of the slit I9 in a vertical direction will affect the film, and movement of the image Ila. horizontally across the slit 19 will form a variable area record 25 on the right side of the track T with the peaks thereof pointing toward the left of the track. As long as each record 23 and 25 is confined to half the track T longitudinally of the film and overshooting is avoided in each recording, the two records will be entirely and separately distinct from each other, and the resulting negative, when developed, will appear as shown in Figure 3 wherein the exposed portions are represented by the areas 23 and 25 and the medial line 21 constitutes the dividing line between the two records. Each record 23 or 25 can thereafter be individually reproduced or in conjunction with the other to produce a combined effect.

In practice, the film F may be run through the recording machine with the stop I in the position shown in Fig. 1 and one complete set of sounds recorded at 23. With this recording finished, the stop I may be moved in the direction of the arrow A (Fig. 1), and the film rewound and again fed through the recording machine to record the second complete set of sounds at 25. To reset the stop in the original position, it is moved back in the direction of the arrow C (Fig. 2). If desired, instead of moving the stop 1 as described, the galvanometer mirror may be suitably biased in well known manner to produce the same effect.

Although I have shown and described one method of carrying out my invention, I am aware that many modifications thereof are possible. For example, two systems, one set as shown in a11ae22 Fig. l and the other set as shown in Fig. 2 may be used simultaneously to record both records 23 and 25 at one time, and they may be energized by separate light sources, as shown, or by a single, common light source. Also, if desired, the peaks of the waves of each record may be pointed in the same direction instead of in opposite directions. Many other modifications will, no doubt, readily suggest themselves to those skilled in the art. I desire, therefore, that my invention shall not be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. The method of forming upon a photographic strip a variable area record of two sets of impulses by means including an apertured light stop and a light slit which cooperate to determine the size of the recording light beam, said light stop aperture having a pair of defined edges, which comprises first recording a complete set of one of said sets of impulses along one longitudinal portion of said strip while employing one of said defined edges to determine an edge of said recording beam, and then recording a complete set of the other of said sets of impulses along another longitudinal portion of said strip while employing the other of said defined edges to determine an edge of said recording beam.

2. The method of forming upon a photographic strip a variable area record of two sets of impulses by means including an apertured light stop and a light slit which cooperate to determine the size of the recording light beam, said light stop aperture having right and left hand edges, which comprises first recording a complete set of one of said sets of impulses along one longitudinal portion of said strip while employing either the right or the left hand edge of said aperture to determine an edge of said recording beam, and then recording a complete set of the other of said sets of impulses along another longitudinal portion of said strip while employing the other of said aperture edges to determine an edge of said recording beam.

3. The method of optically forming a variable area photographic record of two associated sets of sounds by optical means including an apertured light stop and a light slit which cooperate to determine the size of the recording light beam, said light stop aperture having right and left hand edges, which comprises first focusing the light stop sharply on said light slit to form an image of one edge of said aperture midway between one edge of said slit and the center thereof, passing a photosensitive strip through the recorder and recording one of said sets of sounds along a predetermined path longitudinally on said strip, thereafter focusing the light stop sharply on said light slit to form an image of the other edge thereof midway between the opposite end of the light slit and the center thereof, and again passing said photosensitive strip through the recorder and recording the other of said sets of sounds along another path longitudinally on said strip adjacent said first named path.

LAWRENCE T. SACHTLEBEN. 

